Now that I think of it, that's not the way to fix the problems that hoarders create. I mean it's great if they won't mess up the contests, but they're still ruining the game altogether.
So the correct way is to introduce a weekly reset!
Right before the contests servers shut down for a 1 hour maintenance. During that time all the items/gold/diamonds/etc are removed from everyone's backpacks. Only team level, vip level, heroes, equipped items and skins are left as they are.
This way everyone starts fresh, so obviously smart and/or rich players have the opportunity to win contests. Not the hoarders dudes. And all the other problems are solved automatically too.
Since that would obviously make hoarders cry, we need to throw them a bone. All the hoarded stuff before reset gets calculated, and a hoarder receives a certain amoung of "CHEAPSKATE BADGE" items. They will never disappear, so the dudes can still brag to each other, whoever has the most badges.
Seems like a total win-win solution to me.